Question

Study the diagram above and answer the following questions:
(a) How many alleles are involved in blood grouping?

(b) A person having 'AB' blood group has both dominant alleles. What is this inheritance type called?

(c) A man with 'A' blood group marries a woman with 'B' blood group. Can they have a child with 'O' blood group? Explain with the help of a cross.

Hint:

Blood group inheritance involves multiple alleles and codominance. Use Punnett squares to predict possible genotypes.

Answer 1

(a) There are three alleles involved in human ABO blood grouping.

These alleles are:

• I^A – codes for A antigen
• I^B – codes for B antigen
• i – codes for no antigen (O type)

This is an example of multiple alleles, where more than two alleles exist for a genetic trait, but only two are present in an individual at a time.

(b) The inheritance type is called Co-dominance.

In co-dominance, both alleles in a heterozygous individual are fully expressed. In the case of blood group AB:

• The person inherits I^A from one parent and I^B from the other.
• Both A and B antigens are expressed on the surface of red blood cells.

(c) Yes, it is possible for them to have a child with 'O' blood group, depending on their genotypes.

Explanation:

Blood group A can have genotype: I^AI^A or I^Ai
Blood group B can have genotype: I^BI^B or I^Bi

If the man is I^Ai and the woman is I^Bi, the possible cross is:

Father (IAi)	Mother (IBi)	Child Genotype	Child Blood Group
IA	IB	IAIB	AB
IA	i	IAi	A
i	IB	IBi	B
i	i	ii	O

Conclusion: If both parents are heterozygous (I^Ai and I^Bi), there is a 25% chance that the child may inherit i from both parents and have blood group O (genotype: ii).